1. Field of the Invention
The present invention relates to cleaning apparatus for the inner surface of a tank and more particularly to such cleaning apparatus of the type whereby the inner wall surface of a tank is scanned with a sprayed cleaning liquid sprayed from a pair of rotary jet nozzles introduced into the tank.
2. Description of the Prior Art
Tanks of the type carried for example on a railway tank car for the transportation of oils, high-molecular resin raw materials, edible oils, chemical fertilizers or the like has an oblong external appearance and is provided with only a single manhole in the top portion of the substantially central part thereof. In the past, when cleaning the inner surface of such tank, a manual operation has been solely employed so that an operator enters into the tank through the manhole to operate a hand-held water jet nozzle and therefore there has been the disadvantage that the operator is placed in a hazardous environment involving a full possibility of the operator being subjected to the danger of suffocation, poisoning by gas, mechanical injury-and the like, that the efficiency of the operation within the limited tank is deteriorated due to any mechanical interference between the operator itself as well as the hand-held equipment and the tank inner surface, and that there is the danger of any contaminative substance being brought into the tank by the operator itself. These deficiencies are commonly encountered in the case of various containers where a number of dead angles are caused within the container by the external operation alone due to the inadequate positions and number of the manholes, e.g., in the cleaning of flat-type tanks carried on tank lorries and various reaction vessels used in chemical plants.
Japanese Patent Laid-Open Publication No. SHO 54-57215 discloses an apparatus of the type designed for automatically cleaning the inner surface of a horizontal tank without having recourse to any manual operation, said apparatus being provided with a support member which is positioned to fit in an opening formed in the wall surface of a tank, and a rotary jet nozzle which is dependent from the support member to spray a cleaning liquid whereby the rotary jet nozzle is introduced into the tank through the opening to scan the inner wall surface with the cleaning liquid. This known apparatus uses the rotary jet nozzle of the type in which a nozzle head resolving on its axis is caused to orbit about the axis of orbital rotation which is perpendicular to the axis of revolution and its sprayed stream is scanned in all the directions around it. This rotary jet nozzle is arranged at the forward end of the expansion-mechanism which expands and contracts in a telescopic manner. When positioning the support member in the opening of the tank, the expansion mechanism is passed through the opening while being placed in its contracted condition just below the support member and then it is spread out in the longitudinal direction of the tank within the tank thereby placing it in an extended condition. In this way, the rotary jet nozzle introduced into the tank through the top opening is adjusted in position in the longitudinal direction of the horizontal tank within thereof thereby causing a sprayed stream to reach the dead angle positions within the tank.
With this known cleaning apparatus, the telescopic expansion mechanism, the drive unit (the hydraulic cylinder) of the expansion mechanism and the turning unit for spreading out the expansion mechanism between just below the support member and the longitudinal direction of the tank are brought into the tank and their associated mechanisms interfere with the opening in the limited opening of the tank. Thus, it will be extremely difficult to move out these mechanisms to the outside if the expansion mechanism becomes faulty within the tank. Also, due to the fact that the expansion mechanism and the turning unit are independently of each other, they use a large number of component parts and are complicated in construction and it is difficult to discriminate the current rotary position and length of expansion of the expansion mechanism from the outside of the tank. Further, since the expansion mechanism is suspended from the support member into the tank and in this condition it supports at the forward end thereof the rotary jet nozzle in a cantilever manner, when the expansion mechanism is extended, the moment acting on the base portion of the support member due to the reaction force of the rotary jet nozzle is increased rapidly and thus the whole apparatus is caused to vibrate heavily. As a result, there is less possibility of realizing a large-capacity. rotary jet nozzle tending to involve a large spray reaction force and its expansion mechanism tends to easily cause a fault. Still further, the support member must be fastened firmly to the tank for the prevention of vibrations and the structure for supporting the expansion mechanism on the support member is made bulky thus increasing interference of the component members of the cleaning apparatus. Thus, the apparatus of this type cannot be applied to tanks other than those having a considerably large opening.